Origin of Selective Production of Hydrogen Peroxide by Electrochemical Oxygen Reduction
Origin of Selective Production of Hydrogen Peroxide by Electrochemical Oxygen Reduction
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DOI：
10.1021/jacs.1c02186
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发表时间：
2021-06-16
影响因子：
15
通讯作者：
Liu, Yuanyue
中科院分区：
文献类型：
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作者：
Zhao, Xunhua;Liu, Yuanyue
氧还原反应(ORR)是最重要的电化学反应之一。从共同的反应中间体*-O-OH开始，ORR分裂成两条途径，要么通过打破*-O键来产生过氧化氢(H_2O_2)，要么通过打破O-OH键来导致水的形成。然而，令人费解的是，为什么许多催化剂尽管具有强烈的热力学偏好，但对过氧化氢表现出高的选择性。此外，选择性依赖于电势和pH，这一点尚不清楚。在这里，我们发展了一个先进的第一原理模型，用于有效地计算固-水界面的电化学反应动力学，这是传统模型所不能实现的。利用该模型对典型的双氧水生产催化剂进行了研究，发现由于O-OH键的刚性，破坏O-OH键比破坏*-O具有更高的势垒。重要的是，我们揭示了选择性对电势和pH的依赖源于对*-O-OH中前/后O的质子亲和力。对于单钴原子催化剂，降低电势会促进质子对前一个氧的吸附，从而提高H_2O_2的选择性。相反，对于碳催化剂，质子更倾向于后者的O，导致在酸性条件下H_2O_2的选择性较低。这些发现解释了实验，并突出了选择性的动力学根源。我们的工作通过揭示质子亲和力这一新的因素来加深对ORR的理解，并为有效模拟多相电化学的原子水平动力学提供了一个新的模型。
Oxygen reduction reaction (ORR) is one of the most important electrochemical reactions. Starting from a common reaction intermediate *-O-OH, the ORR splits into two pathways, either producing hydrogen peroxide (H2O2) by breaking the *-O bond or leading to water formation by breaking the O-OH bond. However, it is puzzling why many catalysts, despite the strong thermodynamic preference for the O-OH breaking, exhibit high selectivity for hydrogen peroxide. Moreover, the selectivity is dependent on the potential and pH, which remain not understood. Here we develop an advanced first-principles model for effective calculation of the electrochemical reaction kinetics at the solid-water interface, which were not accessible by conventional models. Using this model to study representative catalysts for H2O2 production, we find that breaking the O-OH bond can have a higher energy barrier than breaking *-O, due to the rigidity of the O-OH bond. Importantly, we reveal that the selectivity dependence on potential and pH is rooted into the proton affinity to the former/later O in *-O-OH. For single cobalt atom catalyst, decreasing potential promotes proton adsorption to the former O, thereby increasing the H2O2 selectivity. In contrast, for the carbon catalyst, the proton prefers the latter O, resulting in a lower H2O2 selectivity in acid condition. These findings explain the experiments and highlight the kinetic origins of the selectivity. Our work improves the understanding of ORR by uncovering the proton affinity as a new factor and provides a new model to effectively simulate the atomic-level kinetics of heterogeneous electrochemistry.